Investigation on the thermodynamic calculation of a 35 MWth oxy-fuel combustion coal-fired boiler

Abstract

Oxy-fuel combustion technology is one of the most promising technologies for CO2 capture from coal-fired power plants and is remarkably characterized by the recycled flue gas (RFG). RFGs and pure oxygen are substitute for air, which alter the thermodynamics and heat transfer features for an oxy-fuel combustion coal-fired boiler. Hence, conventional thermodynamic calculation method for air combustion need to be improved for oxy-fuel combustion. This study primarily proposed a modified thermodynamic calculation method, which is subsequently verified by the experimental data for a 35 MWth coal-fired boiler under oxy-fuel combustion with dry and wet recycle modes. Validation results indicate that the modified method could predict the temperatures well in the main heating surfaces of the boiler for oxy-fuel combustion. Given the fine distinction between calculated and experimental temperatures for the main heating surfaces, several key parameters in the main heating surfaces are corrected to improve the precision of the corrected method. Compared with air combustion, the fouling factors for oxy-fuel wet recycle and dry recycle increase, while the effective coefficients and ash deposition coefficients for oxy-fuel combustion reduce. Notably, the utilization coefficients for oxy-fuel are relative to those for air combustion. The heat transfer features in the main heating surfaces are also discussed. Consequently, heat transfer is mainly controlled by the radiative heat transfer of flue gas in the furnace and is determined by the heat capacity of flue gas in the horizontal and vertical heating surfaces under oxy-fuel combustion.